All process conditions were picked to minimize the back-biting termination reaction so the maximum level of living arm could be carried into the core-forming step. Major contributors to control of termination were: 1. Using 0.2% (mole basis) of catalyst on initiator instead of higher concentrations. Within the constraints defined below, this produces a robust process that is insensitive to minor changes in materials, temperatures, and rates of addition. 2. Minimizing the time between arm formation and core formation. Polymerization of arm monomethacrylate to about 96 to 98% before core formation was the aim because conversion to >99% would have allowed too much time for termination to proceed. 3. Adding core-forming monomer (ethylene glycol dimethacrylate) in about 5 min to keep monomer concentration high in this step. Faster add times may not be desirable because of mixing difficulties in this extremely fast polymerization. 4. Reaction solvent mixture containing 50% tetrahydrofuran. This allowed the reflux temperature to be about 85°C. 5. Keeping monomer concentration high in the arm-forming step by starting the polymerization with half of the monomer in the reactor. This forced the polymerization past the trimer stage, where termination is fastest. 6. Starting the reaction at room temperature so the exotherm could be dissipated by the heat capacity of the system. Two lots of trimethylsiloxyethyl methacrylate used to introduce hydroxyl groups into the product (after unblocking) gave different rates of polymerization, with one lot reaching the core-forming step in about half the time of the other. The monomer lot with the higher reactivity also led to higher levels of free arm. Stars made at high (2.0%) catalyst levels were quite unstable to molecular weight and viscosity increase. Mechanistic studies show that the increase is probably because of star/ star free-radical methacrylate polymerization involving pendant residual methacrylate unsaturation from the core-forming step. Stars made under the recommended conditions using 0.2% catalyst and the above process steps are probably stable enough for commercial use.

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Polymers which are multifunctional in epoxide groups were synthesized by copolymerizing glycidyl methacrylate (GMA) with acrylate and vinyl monomers. The reactivity ratios at 65°C. for the monomer pair styrene (M1)–GMA (M2) are r1 = 0.34 ± 0.05 and r2 = 0.63 ± 0.01. Glycidyl methacrylate (GMA) is similar to methyl methacrylate in its copolymerization characteristics. The copolymers can be crosslinked by the same classes of materials that are useful with conventional epoxide resins based on epichlorohydrin and bisphenol A. Similar curing conditions and reactant stoichiometry can also be used. Three GMA copolymers are described: (1) a phosphated styrene/GMA (85/15) copolymer which is thermosetting and can be used as an appliance finish vehicle to yield enamels with excellent resistance properties; (2) an ethyl acrylate/GMA (97/3) elastomer which can be vulcanized with amines or diacids; and (3) a methyl methacrylate/GMA (70/30) copolymer which can be crosslinked at room temperature with amines. These polymers have good resistance to yellowing because of their aliphatic hydrocarbon backbone. The molecular weight and epoxide functionality of the polymers can be varied over wide ranges.

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